This is a plugin I found recently and really enjoy. It gives you the opportunity to redirect several webpages to alternatives. For example Youtube to FreeTube or Piped. If I search for youtube in Firefox, FreeTube automatically opens and shows me my feed. I like it, I use it, I can recommend it.
I agree it it very annoying. I feel it goes against the whole libre and neutrality aspect of why firefox is important. I want the full linux-type experience on every device. :D
As the other comment says, it is possible to get addons in mobile FF . Tbh I have never done it. But I probably will someday.